1. Field of the Invention
The present invention relates to a photodiode cell structure of a photodiode integrated circuit for optical pickup and a method of manufacturing the same, and, more particularly, to a photodiode cell structure of a photodiode integrated circuit (hereinafter, referred to as ‘PDIC’) for optical pickup, in which highly-concentrated impurities are thinly doped between adjacent light-receiving regions and then floated, and thus the adjacent light-receiving regions are isolated from each other, thereby improving the optical efficiency of a photodetector, and a method of manufacturing the same.
2. Description of the Related Art
Generally, a photodetector is a transducer which detects light and then converts its strength into electrical signals. Examples of the photodetector include a photoelectric cell (silicon, selenium), a photoconductive device (cadmium sulfide, cadmium selenide), a photodiode, a phototransistor, a photomultiplier tube, a photoelectric tube (vacuum, gas sealing), and the like. Generally, the photodetector is fabricated using a direct transition semiconductor having excellent light conversion efficiency.
The photodetector has various structures, and generally includes a PIN photodetector using P-N junction, a Schottky photodetector using Schottky junction, a MSM (metal semiconductor metal) photodetector, and the like.
Meanwhile, recently, the importance of lasers and PDICs has been greatly highlighted in the optical data storage field. In order to replay and store optical data in a large-capacity storage medium, the wavelength of a laser must be shortened, and in order to detect the shortened wavelength thereof, the efficiency of a photodetector is required to be increased.
Currently, a photodetector which can detect wavelengths of 650 nm and 780 nm has a PIN structure. In order to increase the efficiency of such a photodetector, it is required to change the cell of a conventional photodetector used in a PDIC to a high-efficiency cell.
FIG. 1 is a plan view showing a conventional PIN-structured photodiode (PD) cell, and FIGS. 2A and 2B are sectional views of the photodiode (PD) cell taken vertically to a substrate along the line A-A′ of FIG. 1, respectively.
In a conventional photodiode cell 100 of a photodiode integrated circuit for optical pickup, as shown in FIGS. 1, 2A and 2B, second-type epitaxial layers 103a and 103b (for example, N-type epitaxial layers), which become intrinsic layers having a P-I-N structure, are formed on a first-type substrate 101a or 101b (for example, a P-type substrate) through an epitaxial growth method. Subsequently, the second-type expitaxial layers 103a and 103b are formed thereon with heavily-doped second type layers 105a-1˜4 and 105b-1˜4 (for example, N+ layers) which are multi-divided light-receiving regions.
The heavily-doped second-type layers 105a-1˜4 and 105b-1˜4 formed in this way must be isolated from each other in order to increase their optical efficiency. For this, a method of completely isolating the heavily-doped second-type layers 105a-1˜4 from each other by physically forming a first-type well 107a (for example, P-well) and a first-type BUR 109b (For example, PBUR) between adjacent heavily-doped second-type layers 105a-1˜4, for example, two adjacent heavily-doped second-type layers 105a-1 and 105a-2 such that they are connected to a substrate 101a has been used (refer to FIG. 2A). However, this method is problematic in that the width of the first-type well 107a is excessively large, so that effective light-receiving regions become small, thereby decreasing optical efficiency.
Alternatively, a method of electrically isolating the heavily-doped second-type layers 105b-1˜4 from each other by forming a first-type well 107b between adjacent heavily-doped second-type layers 105b-1˜4, for example, two adjacent heavily-doped second-type layers 105b-1 and 105b-2 and then grounding the first-type well 107b (refer to FIG. 2B) has been used. However, this method is also problematic in that the first-type well 107b is grounded and thus connected to the ground (GND), so that leakage current is generated, thereby causing noise.